Resistor and method of adjusting resistance

ABSTRACT

A resistor is formed on an insulating support between a pair of electrode terminals, a portion of the resistor extending out of the direct field established between the electrodes. The resistance value is precisely adjusted by removing resistor material in the fringing field.

United States Patent [72] Inventors Darnall P. Burks [50] Field ofSearch 338/ 195, Williamstown; 309, 308; 29/620 John P. Maher, NorthAdams, Mass. [2]] Ap No. 823,350 [56] References Cited [22] Filed May 9,1969 UNITED STATES PATENTS 1 Patented Al"- 6, 1971 3,284,878 11/1966Best 29/620 1 zp Electric p y 3,422,386 1/1969 l-lelgeland 338/309 orthAdams Mass Primary Examiner-E. A. Goldberg Attorneys-Connolly and Hutz,Vincent l-l. Sweeney, James Paul OSullivan and David R. Thornton [54]RESISTOR AND METHOD OF ADJUSTING in ABSTRACT: A resistor is formed on aninsulating support w g between a pair of electrode terminals, a portionof the resistor [52] U.S. Cl 338/309, extending out of the direct fieldestablished between the elec- 29/620, 338/195 trodes. The resistancevalue is precisely adjusted by removing 151] bit. H0lc 7/00 resistormaterial in the fringing field.

Patented April 6, 1971 FIGZ RESISTOR AND METHOD OF ADQUSTING RESISTANCEBACKGROUND OF THE INVENTION This invention relates to thick filmresistors, and more particularly to adjusting deposited thick filmresistors to their final value. t.

Present techniques call for trimming the required resistor material froman area lying in the direct field of the electrodes. Trimming criticallyaffects the resistance value and requires extremely fine trimmingtechniques. Present trimming techniques either result in unacceptabletolerance levels or have percentage of adjustment limitations imposed bythe amount of area available for trimming.

It is therefore an object of the present invention to provide a thickfilm resistor trimmed to a very precise value.

It is a further object to provide a method for accurately adjusting sucha resistor.

It is a still further object to provide such a resistor adjustable to upto 30 percent.

SUMMARY OF THE INVENTION Broadly, this invention provides accurateadjustment of a thick film resistor deposited on a substrate between twoelectrodes. A sufficient amount of the resistor lying outside of thedirect area between the electrodes is provided to permit theestablishment of a fringing field above the direct field establishedbetween the two electrodes.

In one embodiment, the resistor is precisely adjusted by trimming awayresistor material wholly contained within the established fringingfield. In another embodiment, resistor material in both fields istrimmed.

It has been found that removal of resistor material located in thefringing field has less of an effect than removal of the same amount ofmaterial in the direct field i.e., more resistor material must beremoved from the fringing field than in the direct field to effect thesame unit change in resistance. This discovery permits extremely fineadjustments not possible by conventional methods, and also permitslarger percentage adjustments depending on the amount of the availableresistor material in the fringing field.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 shows a top view of aresistor formed according to this invention; and

FIG. 2 illustrates a top view of an alternate embodiment of theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, thecomponent comprises an insulating substrate 11 upon which is positioneda pair of spaced electrodes 12 and 13. Resistor material 14 is depositedbetween the electrodes. A portion 15 of the material 14 lies in thedirect field established between the two electrodes l2, 13 while theremaining portion 16 of the resistor material 14 lies in the fringingfield of the electrodes. The resistor 10 has been adjusted to a desiredvalue by removing a selected area 17 from resistor material portion 16.Since resistor material l6 lies within the fringing field more resistormaterial can be removed per unit change in resistance than if thematerial to be trimmed lay in the direct field. This characteristicpermits an extremely precise resistance adjustment to be made. Actualtrimming may be performedby any desired abrasive technique.

initial rough adjustment is made by cutting away area 20 from resistormaterial 24 in the direct field between electrodes 22 and 23. The fineadjustment is made by trimming away the required amount of material 27from area 26 in the fringing field resistor material.

An example of the silver electrodes is deposited on a substrate of A1O3. Deposited over and between the electrodes as shown in FIG. 1 is aresistance film having a resistivity of LI Kilohms per square. The filmhas approximately 50 percent of its area in the direct electrode fieldwith the remaining area in the gradually weakening electrode fringingfield.

The overall resistance of the unit was originally 820 ohms and it wasdesired to trim the value to l Kilohms with an adjustment tolerance of0.03 percent. Twenty percent of the film lying in the direct field wasremoved by sand abrasion, bringing the resistance to 960 ohms. Then 60percent of the area of the fringing field was removed to bring theresistance to the final value of 1,000 ohms.

We claim:

1. A method of precisely adjusting a thick film resistor which comprisesthe steps of:

positioning a pair of electrode terminal on an insulating substrate;depositing a resistor film on the substrate overlying the area betweensaid electrode terminals and an additional area extending beyond saidarea between said terminals, whereby a direct field is establishedacross the film between the electrodes while a fringing field isestablished across the resistor film lying outside the electrodeencompassing area;

first removing a portion of the resistance film lying in said directfield to cause a rough adjustment in the resistance value; and

second removing a portion of the resistance film lying in said fringingfield so as to adjust to the final desired resistance value.

2. A resistor comprising an insulating support; a pair of electrodeterminals carried by said support; a resistance film on the supporthaving a first portion of nonuniform width extending between and incontact with both of said terminals and across which a direct field willbe established, a second portion of said resistance film extendingbeyond the area confined between the two electrodes and across which afringing field will be established, the extending portion also being ofa nonuniform width, the nonuniform width of the two portion resistancefilm having been made by removing parts of the film for adjustingresistance value.

invention is as follows. A pair of spaced

1. A method of precisely adjusting a thick film resistor which comprisesthe steps of: positioning a pair of electrode terminal on an insulatingsubstrate; depositing a resistor film on the substrate overlying thearea between said electrode terminals and an additional area extendingbeyond said area between said terminals, whereby a direct field isestablished across the film between the electrodes while a fringingfield is established across the resistor film lying outside theelectrode encompassing area; first removing a portion of the resistancefilm lying in said direct field to cause a rough adjustment in theresistance value; and second removing a portion of the resistance filmlying in said fringing field so as to adjust to the final desiredresistance value.
 2. A resistor comprising an insulating support; a pairof electrode terminals carried by said support; a resistance film on thesupport having a first portion of nonuniform width extending between andin contact with both of said terminals and across which a direct fieldwill be established, a second portion of said resistance film extendingbeyond the area confined between the two electrodes and across which afringing field will be established, the extending portion also being ofa nonuniform width, the nonuniform width of the two portion resistancefilm having been made by removing parts of the film for adjustingresistance value.